Objectives The gut microbiota is emerging as an important regulator of cardiovascular health. Indeed, gut dysbiosis is increasingly being linked to the development of cardiovascular disease (CVD). Aging and obesity are associated with the development of CVD largely due to the development of vascular dysfunction, namely endothelial dysfunction and arterial stiffness. The objective of this study was to examine the relationship between the gut microbiota, blood pressure, and vascular function in aging overweight and obese individuals. Methods This cross-sectional study included fifteen overweight and obese (mean body mass index, BMI: 29.5; range: 25.8–37.0) middle-aged/older men and postmenopausal women (mean age: 53; range: 42–64 years). Blood pressure, arterial stiffness (augmentation index, AIx, and aortic pulse wave velocity, aPWV), and endothelial function (reactive hyperemia index, RHI) were assessed. Stool samples were collected for gut microbiota analysis using 16S ribosomal RNA sequencing. Principal coordinates analysis and Pearson's correlations were performed to evaluate the relationship between the gut microbiota and measures of vascular function and blood pressure. Results Global gut microbiota phenotypes clustered most strongly by aPWV (groups separated by median value) as visualized by Non-Metric Dimensional Scaling plot of Bray-Curtis Distances (stress = 0.09; P = 0.07). Several bacterial taxa correlated with vascular parameters. For example, Bifidobacterium longum (r = 0.80, P < 0.001) and Akkermansia muciniphila (r = 0.56, P = 0.047) were positively correlated with RHI. Bifdobacterium bifidum (r = −0.61, P = 0.02) and Oxalobacter formigenes (r = −0.62, P = 0.02) were negatively correlated with systolic blood pressure. Interestingly, there was no significant clustering by BMI groupings (overweight vs. obese) or correlations between BMI and specific taxa. Conclusions These preliminary data suggest that the gut microbiota is linked to vascular dysfunction and increased blood pressure in aging overweight and obese individuals independent of BMI. Further data collection and analysis are currently underway to explore these relationships in a larger human cohort, and to explore underlying mechanisms through transferring of vascular phenotypes in humans to germ-free mice through microbiota transplantation. Funding Sources NIFA, USDA.

Objectives High-fat meal (HFM) consumption has been shown to impair postprandial endothelial function. Red beetroot juice (RBJ) contains polyphenols, betalains, carotenoids, ascorbic acid, and inorganic nitrate, and has been shown to improve endothelial function. This study investigated the acute and chronic effects of RBJ and its bioactive components on postprandial endothelial function. We hypothesized that a HFM would impair postprandial endothelial function, and that RBJ would attenuate this, in part, through increased circulating nitrate/nitrite (NOx) levels. Methods A 4-period randomized, double-blind, placebo-controlled crossover clinical trial was conducted. Fifteen overweight and obese middle-aged/older men and postmenopausal women underwent baseline (T0) assessment of endothelial function (via reactive hyperemia index, RHI) and collection of blood and saliva. Participants consumed one of the following 70 mL treatments (acute exposure): 1) RBJ, 2) nitrate-free RBJ (NF-RBJ), 3) placebo + nitrate (PBO + NIT), and 4) placebo (PBO), followed by a HFM. RHI was measured at 4 hours (T4) post-HFM, and blood and saliva were collected at 1 hour (T1), 2 hours (T2), and T4. Participants then consumed treatments daily for 4 weeks (chronic exposure), and all assessments were repeated before/after the HFM but without consuming treatments. Results No significant time or treatment effects were observed for RHI. Following acute and chronic exposure to RBJ and PBO + NIT, plasma NOx levels were higher at T0 (chronic only), T1, T2, and T4 compared to PBO and NF-RBJ (P < 0.001). After chronic exposure to RBJ, saliva NOx levels were higher at T0, T1, T2, and T4 compared to PBO and NF-RBJ (P < 0.001). Saliva NOx levels for PBO + NIT were higher than both PBO and NF-RBJ at T0 (P < 0.001), but only higher than NF-RBJ at T1 (P = 0.02), and higher than PBO at T4 (P = 0.02). Additionally, there was a time*treatment interaction for plasma and saliva NOx levels following 4 weeks of daily exposure to RBJ and PBO + NIT (P < 0.001). Conclusions The preliminary results of this study suggest that HFM consumption does not significantly impair postprandial endothelial function in this population. In addition, acute and chronic RBJ exposure does not significantly improve endothelial function despite increases in plasma and saliva NOx. Funding Sources Colorado Agricultural Experiment Station, NIFA, USDA.

Objectives Dietary inorganic nitrate from foods such as red beetroot juice (RBJ) can contribute to nitric oxide (NO) bioavailability through the enterosalivary nitrate-nitrite-NO pathway. A critical step in this pathway is the reduction of nitrate to nitrite by oral bacteria. We investigated the effects of inorganic nitrate supplementation, as RBJ or placebo + potassium nitrate (PBO+NIT), on the oral microbiota, and its relationship with saliva and plasma NO metabolites and vascular endothelial function. Methods In a randomized, double-blind, placebo-controlled trial, we measured the abundance of oral nitrate-reducing bacteria in saliva samples from 15 middle-aged/older adults with overweight and obesity using 16 rRNA sequencing. We also assessed the relationship of oral nitrate-reducing bacteria with the physiological responses to acute (4 hours) and chronic (4 weeks) RBJ, PBO+NIT, nitrate-free RBJ, and placebo supplementation via measurement of saliva and plasma nitrate/nitrite (NOx), plasma nitrite levels, and reactive hyperemia index (RHI). Results A significant decrease in the alpha diversity metric, Pileou's Evenness, was detected after chronic consumption of PBO+NIT (0.69 ± 0.05 at week 0 vs. 0.65 ± 0.05 at week 4; P &lt; 0.05), while there was a trend for a decline following RBJ consumption (0.69 ± 0.05 at week 0 vs. 0.65 ± 0.05 at week 4; P = 0.08). No significant differences in abundance of nitrate-reducing bacteria were observed after chronic supplementation, although abundance of the species Neisseria subflava was trending toward an increase in the RBJ group (10.8% at week 0 vs. 12.2% at week 4; P = 0.07). Plasma and saliva NOx increased from baseline and remained elevated for the 4-hour testing period after acute and chronic RBJ and PBO+NIT supplementation (all P &lt; 0.05), while plasma nitrite only peaked at 2 hours in the RBJ group after acute supplementation and was significantly higher than PBO+NIT group (P &lt; 0.01). RHI change from baseline to 4 hours was positively correlated with total abundance of nitrate-reducing species after chronic RBJ supplementation (r = 0.5; P = 0.05). Conclusions Acute and chronic RBJ and PBO+NIT supplementation increases NO metabolites and may alter the oral microbiota to favorably affect vascular endothelial function in middle-aged/older adults with overweight and obesity. Funding Sources NIFA, USDA.